A Canadian army captain who fought alongside American troops in Afghanistan, and who is married to a former officer in the US air force, has been deported as Donald Trump’s zero tolerance immigration policies continue to break apart military families.

Demetry Furman, 47, says he held a top-level security clearance with US forces during his service in the Middle East and worked with them on several successful anti-drugs operations that prevented millions of dollars of heroin coming to the West.

But in a twist of irony he says it was a long-spent 1992 marijuana conviction that led to his being dumped by agents from the Immigration and Customs Enforcement agency (Ice) at the Canadian border on Tuesday – after he spent 77 days in a maximum security jail in Ohio labelled as a drugs trafficker.

“I feel betrayed. It’s a slap in the face because when I was in Afghanistan no-one cared what flag was on my shoulder,” Furman said. “I’m labelled a drug trafficker by them right now, but when I was in Afghanistan and guarding poppy fields, I was stopping opium convoys through Pakistan to China to be made into heroin and shipped to the US.”

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The conviction, which at the time resulted in an $80 fine and 28 days’ community service, came after a passenger in the car he was driving attempted to sell one ounce of marijuana to an undercover policeman. Canadian authorities later vacated the conviction and Furman says he was told by US immigration officials as recently as 2016 that it was no barrier to his application for a green card after he married his wife Cynthia in 2014. They couple had met when they served together in Ohio three years earlier.

But under the Trump administration’s zero tolerance immigration policies, what appeared to be a minor blip on his record has taken on greater significance. Ice agents have widened their scope for deportations, and even military families with clean criminal records have been affected. In August, the wife of a decorated US marine and their nine-year-old daughter were deported to Mexico after years of being told they were not a priority.

The Furmans were similarly assured they were safe while his green card application was being processed. “They interviewed us in Cleveland in 2016 and said everything looks great and we should be getting everything taken care of in the next 30 to 45 days,” said Cynthia Furman, 50.

“I even got a call from Washington and the immigration officer chuckled when I said I was worried my husband would be deported because this is taking so long. He said there’s no need to be worried because we were doing everything right.”

Then, after being told the green card application “had been lost”, Furman was arrested on August 1 at a drivers’ licence office in Medina, Ohio, as he tried to register a truck. The system flagged up his name and officials there called Ice. “I was sitting in the car waiting for him and two Ice agents came up and handed me his keys and his pocket knife and said they were detaining him,” Cynthia Furman said.

“They wouldn’t tell me why, or where they were taking him, and wouldn’t let me see him. I said I couldn’t drive because I had my ankle in a cast and they just said ‘call somebody’ and walked off.”

She said it took several days before she found out where he was, and that he was moved around a couple of county jails before ending up at the maximum security facility with convicted murderers and rapists. She said she was allowed to see him only twice by video chat, and that his health had suffered because of his incarceration in a cell with no windows.

On Tuesday he said, he was shackled and driven with other deportees in a van to the Canadian border, with an Ice agent shaking his hand and wishing him well before driving off.

A phone call and two emails to Ice by the Guardian requesting a comment were not immediately returned, but the Globe and Mail of Canada reported that documents from the Department of Homeland Security highlighted a drugs trafficking conviction for Furman in 1992 and that he was in the US as an undocumented immigrant, which Cynthia Furman denies. “They granted him humanitarian parole to be here three times because of my health and said there was no problem,” she said.

Furman, meanwhile, said he was sleeping on a friend’s sofa in Windsor, Canada, as he figured his next steps, which he said would eventually include hiring an immigration attorney to try to get the deportation order overturned.

“I’m not unique, I’m one of thousands of people this is being done to, other veterans that this is being done to,” he said.

“This has to stop. We believed in our government, we did what our government asked us to do, they sent us to war. And now we’re cannon fodder? No, we’re human beings.”